The whole pretense of the show is sad. At the opening to the show you see nukes in the ground, and throughout the episodes there are broken appliances like washing machines hidden in trees. The show references a 'mushroom war' hinting at nuclear war, and then you realize that Fin is the only human on a planet full of fallout made creatures and the only remnants of people are the Ice King who is technically not human anymore, and mutants living underground in the old cities that were destroyed by the war. The happy-go-lucky adventurer is the only human left on a planet recovering from nuclear war.